Single embryo transfer (SET) is the preferred treatment to limit multiple pregnancies after ART. In order not to compromise the carry home baby rate, the selection of the embryo for transfer in the first cycle becomes even more important. Next to the existing criterion based on morphology, other methods are currently under investigation. The use of quantitative gene expression measurements in cumulus cells (CC), which are in close contact with the oocyte during growth and maturation, seems a promising method (Huang and Wells 2010). Since the first published study on the subject where CC expression could be related to embryo development (McKenzie et al. 2004), several other studies have investigated this possibility and try to relate CC expression to different endpoints. Examples of endpoints investigated are: embryo development (Anderson et al. 2009; Cillo et al. 2007; Feuerstein et al. 2007; Hasegawa et al. 2005; van Montfoort et al. 2008; Zhang et al. 2005), aneuploidy stage of the oocyte (Fragouli et al. 2012b), oocyte nuclear maturity stage (Ouandaogo et al. 2011) and probably the most important from a patient perspective: pregnancy outcome (Assidi et al. 2011; Assou et al. 2008; Gebhardt et al. 2011; Wathlet et al. 2012; Wathlet et al. 2011). Confirmation of results between different studies does not seem obvious in the analysis of CC gene expression. In the current literature not many genes were found in common in different studies. For example, hyaluronan synthase 2 (HAS2) was higher expressed in good quality embryos compared to low embryo morphology in two studies (Cillo et al. 2007; McKenzie et al. 2004), but could not be related to embryo morphology in two other studies (Anderson et al. 2009; Gebhardt et al. 2011). Divergences can be due to a different experimental design, with different endpoints, but gene expression can be influenced by known factors such as the stimulation protocol of the patients (Adriaenssens et al. 2009; Adriaenssens et al. 2010; Grondahl et al. 2009) or not yet assessed factors such as culture media used in the different IVF laboratories.
In this study, 47 individual cumulus complexes from 47 Intra-cytoplasmic sperm injection (ICSI) patients were retrospectively analyzed with quantitative real-time polymerase chain reaction (QPCR). Using the current sample set, a pregnancy prediction model from a previous study (Wathlet et al. 2012) was validated for its predictive power. In a next step, in an attempt to search for new genes with a stronger predictive power, new multiparametric models were built considering the 3 genes (ephrin-B2 (EFNB2), calcium/calmodulin-dependent protein kinase ID (CAMK1D), stanniocalcin 1 (STC1)) described earlier and multiple novel genes and splice variants of said genes in mathematical models to predict the oocyte competence (see Tables).
Our patient sample set allowed for an analysis never reported before in literature: CC from oocytes that did not result in pregnancy in the fresh transfer cycle and the CC from their sibling oocytes that resulted in pregnancy after a frozen embryo transfer (FRET) cycle were analyzed (Intra-patient analysis). To our knowledge this is the first study to compare pregnant and non-pregnant CC from the same retrieval cycle in a SET setting as would be done in a final clinical application.